NK - natural killer identifies the abnormalities on cells by detecting the amount of a. MHC I molecules b. Non self molecules c. PAMP -pathogen-associated molecular patterns d. PRR-pattern recognition receptors

The correct answer is a. MHC I molecules.<br /><br />Natural killer (NK) cells are a type of cytotoxic lymphocyte that play a crucial role in the innate immune system. They are responsible for identifying and eliminating abnormal cells, such as tumor cells or virus-infected cells, in the body.<br /><br />NK cells recognize abnormalities on cells by detecting the amount of major histocompatibility complex (MHC) class I molecules on the surface of the target cells. MHC class I molecules are proteins that present pieces of proteins from within the cell to the NK cell. Normal cells typically have a high expression of MHC class I molecules, while abnormal cells often have a reduced expression or downregulation of these molecules.<br /><br />By detecting the absence or reduction of MHC class I molecules on the surface of target cells, NK cells can recognize and eliminate these abnormal cells without the need for prior sensitization or activation. This mechanism allows NK cells to provide an immediate defense against infections and tumor development.